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<TITLE>Error Indication by Stream Iterators</TITLE>
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<H2>43.3 Error Indication by Stream Iterators</H2>
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<P>The <B><I><A HREF="../stdlibref/basic-istream.html">istream</A></I></B> and <B><I><A HREF="../stdlibref/basic-ostream.html">ostream</A></I></B> iterators by themselves have no means of indicating the success or failure of an operation. The stream being operated on should be probed for<SAMP> good()</SAMP>, <SAMP>eof()</SAMP>, <SAMP>fail()</SAMP>, or <SAMP>bad()</SAMP> conditions. This is convenient, as stream state can be checked for exception conditions that were set in <B><I><A HREF="../stdlibref/basic-ios.html">basic_ios</A></I></B> (using the member function <SAMP>exceptions(iostate)</SAMP>) after each input or output operation.</P>

<UL><PRE>
void print()
{
   std::ostream_iterator&lt;int, char, char_traits&lt;char&gt; &gt; os(cout);

   try {
      std::cout.exceptions (std::ios::failbit | std::ios::badbit);
      *os = 3;  //output `3'
      os++;  // receive next output
   }
   catch(std::ios_base::failure&amp; emsg) {
      std::cerr&lt;&lt;emsg.what();
   }
}
</PRE></UL>
<P>Since stream buffers do not retain information about the success or failure of operations, <B><I><A HREF="../stdlibref/basic-streambuf.html">streambuf</A></I></B> iterators provide a member function, <SAMP>failed()</SAMP>, to indicate success or failure in a preceding operation on the stream buffer. </P>

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